1. Field of the Invention
The present invention relates to a semiconductor storage device, and more particularly to a device in which the voltage of word-lines is boosted up in order to store and hold information securely for use in the field of, for example, semiconductor memory devices, to thereby complete a read or write operation.
2. Description of the Related Art
In recent years, with an advancement of information processing devices such as computers, a large number of types of semiconductor storage devices, represented by semiconductor memories such as, for example, RAM (random access memory), ROM (read only momemory) and the like, have been developed.
Nevertheless, with an increase in the speed of operation of such devices in recent computers, semiconductor memories using a higher clock speed have been used particularly in CPUs (central processing units). However, no conventional semiconductor memory can equal the processing speed of the CPU.
Therefore, it is required that a semiconductor memory having a high speed comparable to the speed of the CPU be developed.
The prior art technology of boosting the voltage of the word-lines is that a plurality of word-lines is not selected simultaneously, but that a memory cell is divided into several blocks and only one word-line is selected in each block. That is to say, if one word-line voltage boost generator circuit is provided for every block unit, the loads are comparatively small and the word-line boost generator circuit can be easily driven.
Nevertheless, the word-line load has generally increased due to the high density of recent semiconductor integrated circuits. When the word-line boost generator circuit cannot be realized due to restrictions in the layout or when it is necessary for a memory to select a plurality of word-lines simultaneously, the prior art tends to hinder any further gain in speed and efficiency.
That is to say, when the word-line load increases, the delay in boosting the word-line voltage level potential (V.sub.cc +V.sub.th) makes it difficult to reach the goal of high speed operation by boosting the word-line voltage.